1. Field of the Invention
The present invention relates to a process for producing a semiconductor device having a multilayer interconnection composed of a plurality of conductive layers electrically separated from each other in an area other than the sites at which conductive layers are electrically interconnected via a through hole.
2. Description of the Related Art
Most semiconductor devices have a layer such as a TiN (titanium nitride) film formed on a conductive layer, such as an Al(aluminum)-interconnection, to prevent stress- and/or electro-migration of the conductive layer. In a semiconductor device having a multilayer interconnection composed of a plurality of conductive layers electrically separated from each other, the necessary interconnections between these conductive layers are effected through a through hole formed in an interlayer insulating layer inserted between and electrically separating the conductive layers.
Referring to FIG. 1, in a process for producing a semiconductor device on a semiconductor substrate 201 having an insulation substrate 202 formed thereon, a through hole is conventionally formed in the following manner: an Al conductive layer 20 and an overlying TiN layer 21 are uniformly covered with a SiO.sub.2 (silicon oxide) hillock-preventing insulating layer 22; a flattening insulating layer 23 and a PSG (phosphosilicate glass) layer 24 are then formed, in that order (FIG. 1 (a)); and the SiO.sub.2 and the PSG layers 22, 24 are patterned by a photoetching method using a photoresist 25, to open a through hole 26 (FIG. 1 (b)).
A fluorine-based gas is usually used as an etchant to form the through hole 26 and, during the etching, the TiN layer 21 is also etched and the through hole 26 also extends through the TiN layer 21. TiN is etched by the fluorine-based gas at a relatively higher rate than the SiO.sub.2 or PSG of the layers 22 or 24, and thus a sideways etching of the TiN layer 21 is excessive, with the result that the SiO.sub.2 and the PSG layers 22, 24 overhang the TiN layer 21, i.e., a side groove 27 is formed between the TiN layer 21 and the SiO.sub.2 layer 22, or the through hole 26 has a broadened bottom.
In a subsequent process step, when a conductive substance 28 is filled in the through hole 26 and a heat treatment is carried out, a residue possibly present within the side groove 27 is evaporated and diffused spread to an interface between the Al conductive layer 20 and the filled conductor 28, to cause a problem in that the contact resistance between these two conductors 20 and 28, and in turn two conductive layer, is undesirably increased.